The present invention relates to a tensioning apparatus for a wire net in a vibration sieving machine that is available for sieving of pulverized or granular materials such as agricultural products, minerals or the like.
Heretofore, in such type of machines generally used in the prior art, wire nets are mounted on a frame provided with a vibration device in a tensioned state. As to the method for mounting the wire nets on the frame, hooks are provided at the opposite ends of each wire net, hooks at one end of the wire net are engaged with latches provided on the frame, hooks at the other end of the wire net are engaged with other latches which are provided movably on the same frame, and the wire net is tensioned by pulling the latter movable latches in the direction opposite to the former fixed latches by means of a hydraulic device provided on the frame, which device consists of a piston, a cylinder and the like and makes use of a hydraulic pressure. Under the condition where the wire net has been tensioned in the above-described manner, the vibration device is operated while a raw material to be sieved is being fed onto the wire net, and thereby sieving of agricultural materials, minerals, or the like can be achieved.
If the above-mentioned sieving operation is continued over a long period of time, then in the wire net, blocking of the meshes of the net would be caused by the raw material, and hence the operation efficiency is lowered. In such a case, feeding of the raw material is stopped, and also the operation of the above-described hydraulic device which holds the wire net in a tensioned state, is interrupted. Then, the wire net which has been tensioned hitherto is relaxed at once, hence the distance between adjacent wires in the wire net is broadened, and since the vibration is still continued even under the relaxed state, particles of the pulverized or glanular material which caused the blocking of the wire net are shaken off. Once this shaking off operation has been finished, immediately the wire net is tensioned again by operating the above-described hydraulic device, the raw material is fed again, and thereby the sieving operation is recommenced. As described above, of the sieving machine in the prior art, blocking of the meshes of the wire net can be easily cleared, and so, the sieving machine has been widely used.
However, while the sieving machine of the prior art had the above-described excellent feature, on the other hand it has the following difficulty. That is, the difficulty exists in that as descibed above, during the operation of the sieving machine the hydraulic device must be always kept operating to hold the wire net in a tensioned state. To that end, hydraulic power for actuating the hydraulic device is continuously necessary during the operation of the sieving machine.